The.Köln.Revelations
This YouTube video, about Keith Jarrett's "The Köln Concert", answers and explains a few questions I've passively had about its recording, but I'd just unconciously explained away as part of the nature of improvisation, if you get my meaning. When rules are set aside in order to just play, to just flow, then anything is fair game – including (but not limited to) using the piano itself as a drum in some places.
I'm certain that my dad, who loved this album so much he named me after the pianist, did not know most of what happened around its recording, and I wish I could tell him.